1. Field of the Invention
The present invention relates to a protection device for a tool in tire assembling-disassembling machine, particularly, but not exclusively, suitable for tools having a working slot or groove.
2. Description of Related Art
As it is known, assembling-disassembling of tire onto or from a wheel rim is carried out by fixing the wheel rim to a rotatable support of a tire assembling-disassembling machine and by making use of a tool that has a working slot or groove and is secured to the distal end of a suitable tool-carrying arm carried by a frame component of the tire assembling-disassembling machine. The tool is then slidingly inserted between the wheel rim edge and the tire bead edge. Thus, when the rotatable support is set in rotation, the wheel rim edge slidably engages with the tool working slot or groove, whereas a suitably shaped outer surface of the tool causes the tire bead edge to be transferred progressively from the inner to the outer side of the wheel rim edge or vice versa depending upon the direction of rotation of the rotatable support.
Tire assembling-disassembling tools are made either of a relatively hard metal alloy material or of a relatively soft synthetic material, preferably polyamide, e.g. Nylon®, either alone or reinforced with fibers, e.g. glass fibers, carbon fibers, or the like, in order to ensure a higher flexural-torsional stiffness to better withstand dynamic stress generated, in use, on the one hand, by forced sliding of the tire edge onto the tool outer surface and, on the other, owing to the tire peripheral edge sliding within the tool working slot or groove. Clearly, as the tire edge slides onto the tool outer surface, a resultant of forces is generated which is radially directed with respect to wheel rim, and causes a substantial rise in pressure and thus in friction between surface of the tool working groove or slot and peripheral edge of the wheel rim C set in rotation by the rotatable support of the tire assembling-disassembling machine.
Depending upon the type of wheel rim, i.e. made either of painted light alloy or of steel, friction between the peripheral edge of the wheel rim and the working slot or groove of the tool causes either wear of the tool or scratching of the wheel rim. As a matter of fact, should the wheel rim be made of painted light alloy, sliding of the relatively hard body of the tool onto a portion of the outer peripheral surface of the wheel rim can result in scratching or even damaging the wheel rim, whereas in the case of a steel wheel rim, unless the employed tool is highly resistant it can be rapidly worn off and thus permanently damaged. Should the tool employed in a tire assembling-disassembling operation be new, sliding of the working slot or groove onto the outer peripheral edge of the wheel rim of light alloy does not normally cause any damage; on the contrary, in the case in which the tool was previously used many times onto old and usually deformed steel wheel rim, its groove or slot surface could be deeply scratched which result in the formation of portions in relief, possible debris and/or dust that will scratch the paint on the wheel rim made of light alloy in future maintenance operations. For this reason, the choice of the tool material is normally the result of a compromise of a number of various requirements none of which is fully fulfilled.
In order to overcome these drawbacks, as it is known, it has already been proposed to provide the tire assembling-disassembling machines with two interchangeable tools, one made of plastic material suitable for light alloy wheel rims and the other made of metal alloy suitable for steel wheel rims. Nevertheless, although versatility of the tire assembling-disassembling machines is increased, the operator still has to face the inconvenience of selecting a suitable tool each time.